In diesel engines, the injection of fuel into the combustion chamber is produced in a very short time interval. In general, the fuel injection occurs as a pulse having a duration of a few milliseconds, with a typical duration of about one millisecond for a four cylinder, four cycle engine operating at full speed. Thus, the duration of the injection pulse is short compared with the duration of one crankshaft revolution. In the prior art, the timing of the injection pulse, i.e. the crankshaft angle at which it is initiated, is controlled in accordance with engine operating parameters. Also, the quantity of fuel in each injection pulse is controlled according to engine operating parameters. In order to further enhance engine performance, there remains a need for further control of the injection pulse, namely, the control of the pulse shape. Heretofore, the shape of the fuel pulse, i.e. the fuel flow rate as a function of time, has not been correlated in a controlled manner with engine operating conditions.
In the idealized diesel engine cycle, combustion occurs at constant pressure, i.e. there is a constant pressure burning of the fuel. It is known that so-called constant pressure burn can be achieved by providing fuel injection in which the flow rate of fuel increases linearly with time. Accordingly, it is desirable to produce injection pulses which are of ramp shape. Further, it is desirable to cause the slope of the fuel pulse ramp i.e. the flow ramp rate, to increase with engine speed according to a predetermined relationship.